1. Field of the Invention
This invention relates to a process for the continuous production of fatty acid soaps by reaction of fatty acids with solid metal compounds selected from the series of oxides, hydroxides, hydrogen carbonates and carbonates of metals from the group formed by alkaline earth metals, such as magnesium, calcium and barium, and by lead, aluminum, zinc, cobalt, iron, cadmium and zirconium, optionally in the presence of up to 10% by weight water, based on the total weight of the reactants.
2. Statement of Related Art
The fatty acid soaps to be produced in accordance with the invention are understood to be compounds which are formed by neutralization of fatty acids with stoichiometric quantities of metal oxides, hydroxides, hydrogen carbonates and carbonates or with an excess of these basic metal compounds. Metal soaps are used for many purposes. Calcium soaps, particularly basic calcium soaps, for example soybean oil fatty acid and palm oil fatty acid calcium soaps, are used for the feeding of ruminants; dibasic lead stearate and complex metal/calcium stearates are known additives for the processing of PVC.
Metal soaps can be produced in batches by reaction of a molten fatty acid with a suspension or solution of metal oxides or hydroxides and then filtering and drying the soaps formed. However, this process is complex because the reaction mixture must be diluted sufficiently to remain stirrable. In addition, considerable energy is consumed in drying the soap to a free-flowing product.
Some basic soaps, for example basic lead stearates, can be produced molten in batches, by introducing the metal oxide or hydroxide into a stirred melt of the fatty acid. In processes such as these, product discoloration can occur as a result of the prolonged heating involved. The basic soaps of alkaline earth metals cannont be produced by this process since they are infusible materials.
Other basic soaps, for example the calcium soap of palm oil fatty acid, can be produced in batches in a so-called heating mixer (fluid mixer), of the type normally used in the processing of PVC, by introducing the metal oxide or hydroxide into the molten fatty acid. The temperature of the reaction mixture rises and the water of reaction partially evaporates under the effect of the heat of neutralization and the energy introduced by the mixer. After the starting materials have fully reacted, the reaction mixture changes from a viscous material to a solid. This solid material may be cooled and size-reduced. During the change from the viscous phase to the solid phase, however, the mixer begins to vibrate to an extent which cannot be controlled in a reactor of a few 100 liters capacity which is required for commercial production. In addition, the fluid mixers mentioned above are known for their high consumption of electricity. Accordingly, the process in question is only suitable for the production of small quantities in laboratories and pilot plants.
EP-A 0 163 395 describes a process for the production of metal soaps, in which a pumpable mixture is prepared from molten fatty acids and basic metal compounds, such as calcium oxide, and is spread out over a conveyor belt to complete the reaction and to remove the water formed during the reaction. The reaction product obtained has to be size-reduced which poses technological problems in view of the large quantities to be handled and the solid consistency of the fully reacted fatty acid soaps.